From German Patent Disclosure Documents DE-OS No. 28 42 892 and DE-OS No. 29 03 638, monitoring devices for program controlled equipment are known which recognize short duration disturbances or system breakdowns and thereupon actuate a reset or interrupt input of a microprocessor. This stops the then-running program, which by resetting is put back into proper operation at the beginning of the program, so that an emergency circuit arrangement can be actuated. In such an arrangement, it is a problem that it is impossible to distinguish whether a reset has been brought about by the monitoring device (so-called "watchdog reset") or by other causes, for instance by switching on the supply voltage (so-called "power-on-reset").
In order to attain a definite status after switching on the supply voltage, from which status a normal program course can be started, the emergency circuit arrangement must first be connected to the microprocessor after a stable microprocessor state has been attained. Because of circuitry or program controlled provisions, it is necessary for the connection of the monitoring device to take place in such a way that a reset signal of the monitoring device will not immediately stop the microprocessor and start it up again.
From German Patent Disclosure Document DE-OS No. 32 40 704, a circuit arrangement for monitoring computer elements is know which, for longer-lasting disturbances, keeps attempting to restart the program of the element by means of reset signals. Here also, the problem exists that it is impossible to distinguish between a reset caused by switching on the power, or by the actuation of a reset key, and a reset brought about by a monitoring device.